This invention relates to a method for controlling exhaust gases in an oxygen blown converter.
In steel making in a converter using oxygen, as it is known, a method has been employed to recover combustible gases, such as carbon monoxide (CO) produced by blast refining, in the unburnt state for re-use as heat source.
The unburnt gases have been recovered by employment of a method in which the pressure differential between the throat pressure i.e. the pressure within the hood, and atmospheric pressure is detected, and an exhaust gas damper is automatically adjusted through an adjusting meter or regulator so that said pressure differential assumes a predetermined value. This method, however, unavoidably poses problems such as the so-called blow-out, in which the exhaust gases are emitted from the throat, and the so-called intake phenomenon, in which surplus air is sucked into the throat, due to a delay in detection or in transmission of signals due to rapid variations in the quantity of exhaust gases and a delay in response of the adjusting meter or the exhaust gas damper when the quantity or flow rate of the oxygen fed is changed, when a secondary material such as iron ore etc. is charged or completed to be charged, or when the quantity or feeding rate of a secondary raw material charge is changed in the case where the absolute quantity of the charge is changed. This results in a waste of unburnt exhaust gases and a considerable economic loss due to the wasteful burning of the exhaust gases resulting from intake of surplus air.
Thus, in the oxygen blown converter, a method has been employed in an effort to recover these combustible gases in an unburnt state, the method normally being called the method for recovering unburnt exhaust gases. For example, see the method of British Patent No. 1,187,530. In this method a controlling means therefor, generally called the throat pressure control, is used in which the pressure differential between the throat pressure, i.e., the pressure within the hood of the converter, and atmospheric pressure is detected and the operation of a damper is controlled so that said differential pressure assumes a predetermined level.
Incidentally, a method is employed to suck surplus air by suitably opening the dust collector damper in order to avoid the surging phenomenon of the draught fan for the exhaust gases despite the fact that the furnace generated gases are in very small amount at the early stage and at the last stage of the blast refining operation in the converter. This method, however, results in a wasteful burning of unburnt gases, leading to a considerable economic loss.
Further, the aforementioned throat pressure controlling method unavoidably involves delays in the detection or transmission of signals and delays in the response of the control means or of the damper drive means to a rapid change in converter reaction thereby inevitably producing the blow-out phenomenon, in which the combustible gases are emitted from the throat, or the excessive intake phenomenon, in which surplus air is sucked into the throat, often resulting in an economic loss such as dissipation or wasteful burning of the combustible gases. In addition the blow-out phenomenon is known to produce emission of red fumes, which is not desirable in terms of environmental health.